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ChapterINTRODUCTION
As the world is advancing forth technically in the field of space research,
missile and nuclear industry; very complicated and precise components having some
special requirements are demanded by these industries. The challenge is taken by the
new developments taking place in the manufacturing field. The wordunconventional is used in the sense that the materials like Hastalloy, itralloy,
imonics etc. are such that they can!t be machined by conventional methods but
require some special techniques. The conventional methods, in spite of recent
advancements are inadequate to machine such materials from stand point of
economic production.
The unconventional methods of machining have several specific advantages
over conventional methods of machining and these promise formidable tasks to be
under taken and set a new record in the manufacturing technology. These methods
are not limited by hardness, toughness, and brittleness of materials and can produce
any intricate shape on any work piece material by suitable control over the various
physical parameters of the process. However unconventional methods are not
substitutes for conventional machining methods, but are only complementing them.
on conventional energies are classified according to the nature of the
energy employed in machining
"i# Thermal and $lectro thermal
"ii# %hemical and $lectro %hemical
"iii# &echanical
'n thermal and electro thermal methods, heat energy is concentrated on small
areas of the work piece, to melt and vapori(e the tiny bits of work material. The
)
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required shape is machined by repetition of this process. "$.*.&, +..&., -.A.&,
$..&., '..&.#. 'n chemical and electrochemical machining the work piece material
in contact with a chemical solution is etched "anodic dissolution# in a controlled
manner "$.%.&., $.%.., $.%.H., and $.%.*.#. 'n mechanical methods the material is
removed by mechanical erosion of the work piece material "/.0.&., A..&., and
2..&.#
There are various unconventional machining processes like
$lectro discharge machining
$lectro chemical milling
$lectro chemical grinding -lasma arc machining
+aser beam machining
Abrasive 3et machining
2ater 3et machining
/ltrasonic machining
Abrasive 3et machining is one of the unconventional machining process by
which the material is removed by the erosion of high velocity abrasive particles
mi4ed with gas. And it is a process which is suited for machining super alloys and
refractory type materials.
'n this pro3ect work an attempt has been made to study the abrasive 3et
machining process and fabrication the e4perimental setup used for the abrasive 3et
machining process. And in this study it is observed that the various process
parameters like velocity of 3et, no((le diameter, and abrasive particle si(e. 0tand off
distance will affect the metal removal rate and surface finish of the work piece
material.
5
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LITERATURE SURVEY
6
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Chapter 2LITERATURE SURVEY
/nconventional methods of machining have several specific advantages over
conventional methods of machining. These methods are not limited by hardness,
toughness, and brittleness of materials and can produce any intricate shape on any
work piece material by suitable control over various physical parameters of the
processes. However unconventional methods are not substitutes for conventional
machining methods, but are only complimenting them.
).1 *'77$8$T T9-$0 :7 /%:$T':A+ &$TH:*0
).1.1$+$%T8: %H$&'%A+ &A%H'' "$.%.
This process is developed on the principle of faraday and ohm. 'n this
process, an electrolytic cell is formed by the anode "work piece# and the cathode
"tool# in the midst of a following electrolyte. The metal is removed by the controlled
dissolution of the anode according to the well
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2hen the electrodes are connected to about )>v electric supply source. 7low of
current in the electrolyte is established due to positively changed ions being attracted
towards the cathode and ice versa. %urrent density depends on the rate at which
ions arrive at respective electrodes which is proportional to the applied voltage,
concentration of electrolyte, and gap between the electrodes. *ue to electrolysis
process at the cathode, hydro4yl "
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).1.5 %H$&'%A+ &'++'
This is a form of etching process. 'n this process hob is first cleaned properly
and then some sort of preventive coating is applied "masking# on that particular
portion which is not to be machined. The preventive coating is of vinyl plastic. This
is applied with the help of a template then the 3ob is e4posed to the etching material.
%hemical etching reagent depends upon work material. 7or aluminum it is caustic
soda, and for steel it is acid "itric#. The metal is removed by the chemical
conversions of the metal in to metallic salt
).1.6 +A0$8 $A& &A%H''
+aser is as electro magnetic radiation. 't produces monochromatic light
which is in the form of collimated beam. Though has been introduced recently but is
making much heal way in industry. 't finds user for micro drilling, micro welding
etc. however it has low efficiency and high energy input requirements.
+ight Amplification by 0timulated $mission of 8adiation is called
+.A.0.$.8. beam. 'n this process use is made of laser beam.
$lectrons are arranged in different cells in as atom and each cell has a set
number of electrons. 'f any atom so e4cited, i.e. we pump some amount of e4ternal
energy then the atomic cell will be in e4cited condition and some electrons will
3ump up to ne4t energy level i.e. electrons 3ump from one orbit to ne4t one.
).1.= /+T8A0:'% &A%H'' "/.0.&.#
/ltrasonic waves are sound waves which propagate at frequency of 1B to 5>
kcCsec and are there beyond the human ear to respond. o heat is generated in case
of ultrasonic machining and it provides better working performance. These
processes is best suited for machining circular and non circular holes in hard to
machine and brittle metals whether conducting or non< conducting. /ltrasonic
waves can be generated by pie(oelectric or magneto stricture effects.
).1.@ $+$%T8: $A& &A%H'' "$..&.#
D
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'n this process, the material is removed with the help of a high velocity
"traveling at half the speed of light i.e. 1@>,>>> kmCsec#. 7ocused stream of electrons
which are focused magnetically upon a very small area. These heat and raise the
temperature locally above the boiling point and this melt and vapori(e the work
material at the point of bombardment. This process is best suited for micro cutting of
material because the evaporated area is a function of the bean power and the method
of focusing which can be easily controlled.
The electrons are obtained in 7ree 0tate by heating the cathode. &etal is
vacuum to the temperature at which they attain sufficient speed for escaping to the
space around the cathode. These can then be made to move under the effect of
electric or magnetic field and can be accelerated greatly. The acceleration is carried
out by electric field and focusing and concentration is done by controllable magnetic
fields.
).1.D A8A0'$ $T &A%H''
'n this process a focused stream of abrasive particles carried by high pressure
gas or air at a velocity of about )>> to 6>> mCsec is made to impinge on the work
surface through a o((le, and the work material is removed by erosion by the high
velocity of abrasive material removal rate which depends on flow rate and si(e of
abrasive particles. This process is best suited for machining super alloys and
refractory type of materials, and also machining thin sections of hard materials and
making intricate hard holes.
).1.B A8A0'$ 2AT$8 $T &A%H''
A narrow focused, water 3et is mi4ed with abrasive particles. This 3et is
sprayed with very high pressure resulting in high velocities that cut through all
materials. The water 3et reduces cutting forces and virtually eliminates heating. The
basic cutting mechanism is erosion.
on contact and no tool wear. ood for materials that canEt stand high
B
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temperatures of other methods for stress distortion or metallurgical reasons.
*eveloped in 1F@>Es. Typical pressures are 1>> k -si. +ower pressures are good
for soft materials and metals need higher pressures. The required 3et pressure
decreases with the use of harder abrasives. 0teel plates over 5G thick can be cut.
An abrasive water 3et is a 3et of water, which contains abrasive material.
/sually the water e4its a no((le at a high speed and the abrasive material is in3ected
into the 3et stream. This process is some times known as entrainment in that the
abrasive particles become part of the moving water much as passengers become part
of a moving train. Hence as with a train the water 3et becomes the moving
mechanism.
Abrasive 3et users need in
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7ig ).5? et formation geometry
).).) 2AT$8 -8:-$8T'$0
2ater is a liquid usually regarded as being incompressible, and this is a
sound statement at most ordinary pressures. However, at the high pressures used for
driving an abrasive 3et, water compresses up to 11 percent. The compression
percentage at pressures up to 1>>,>>> pounds per square inch "-0'#.
7or the mathematically inclined, the empirical equation is given by
ecause of the compressibility factor, a pump plunger pumping at =>,>>>
-0' moves at least 1> percent of its stroke length before any water begins to e4it the
check valve. 'f the pump cylinder contains any dead volume, an even greater force is
required.
At the end of the stroke, the dead volume is filled with energy containing
compressed water. -ump mechanical efficiency depends on how well this stored
energy is recovered.
1>
#1.)"........#>>>,=5C1" 1@).>
> eqp+=
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The two main pump types on the marketcrank drive and intensifierdiffer
in the ability to recover this energy. %rank drive pumps recover the e4panding
waterEs energy 3ust like an engine recovers e4panding hot gas energy. 'n the
hydraulically driven plunger of an intensifier pump, the energy is dumped as heat
into the hydraulic oil.
%ompressibility is useful in smoothing out pulsation from the pumping
equipment. 'ntensifier pumps typically pulse at about once per second with quite
large pulses and use an accumulator comprising about )>> cubic inches of fi4ed
water volume. The waterEs compressibility keeps the 3et running during the
intensifierEs plunger reversal cycle.
Three
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from >.@ to >.D. The uncertainty and variability in this value more than masks the
compressibility effects mentioned previously.
0ome literature refers to the orifice coefficient as orifice efficiency, but this
gives the false impression that it is in some way related to energy efficiency. 'n fact,
the orifice almost perfectly converts pressure energy into the waterEs kinetic energy,
with the orifice coefficient affecting only the amount of water flowing through its
effect on the stream diameter.
The amount of water flowing, J, simply is the stream area times the stream
speed. /nfortunately, we usually know the hole si(e rather than the stream si(e, so
the orifice coefficient is used to ratio the hole area down to the stream area. The
equation for the flow through an orifice is?
Assuming inches for the hole diameter, -0' for pressure, -& for flow, and
the liquid is water, the equation is?
This equation predicts the flow to within a few percent, with the ma3or uncertainty
coming from the orifice coefficient. The power required to force the water through
the no((le is calculated as the product of the upstream pressure and the flow rate.
2hen we use -0', -&, and horsepower as units of measure, the equation for
no((le power is?
1)
#).)"...........C)6C ) eqpdpCQ d =
#5.)"..............B6).)F ) eqpdCQ d=
#6.)".............5.1D16C. eqQppowerhorse =
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7ig ).6? ariation of flow rate with pressure and flow rate
The relationships among pressure, flow, no((le si(e, and no((le power are
such that if any two of the quantities are known, the other two can be calculated.
These relationships are shown graphically in 7igure ).6. The stream horsepower
entering the mi4ing tube top affects the cutting rate.
).).6 &'K' T/$ A* %/TT' -8:%$00
As discussed, the power required to drive the 3et is independent of what
occurs with the 3et in the mi4ing tube and below. The mi4ing tube and cutting
process usually are treated as a single phenomenon to be investigated by e4periment.
15
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This important second half of the flow process is described by empirical results
rather than results from engineering calculations. 'n a publicly reported study by
Ieng, 1 result was gathered from a large series of e4periments and equations were
fitted to the data, resulting in the equation?
2here
- Lstagnation pressure of water 3et in -0', typically =>,>>> -0'
d L orifice diameter in inches, typically >.>16 in.
&a L abrasive flow rate in lb.Cmin., typically >.B lb.Cmin.
fa L abrasive factor "1.> for garnet#
J L quality desired. 0et to 1.> for calculating separation speed
H L material thickness in inches
*m L mi4ing tube diameter in inches, typically >.>5> to >.>6> in.
L traverse speed in '-&
& L material machinability
Table 2.1
&achinability, &, of arious
&aterials
Hardened Tool 0teel
&ild 0teel
%opper
Titanium
Aluminum
B>
BD
11>
11=
)1
/nlike the previous equations, this one is valid only for parameters near to
those tested e4perimentally, as listed above. This relatively simple equation
summari(es the results from many test cutting hours, but says nothing about the
detailed behavior of the 3et, other than its ability to cut various materials, nor does it
provide an e4planation of why things are as they are.
16
#=.)"...........1@5
1=.1
@1B.>
565.>5D6.1=F6.1
eqDmHQ
MadMpfaV
=
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-rocesses within the mi4ing tube are very comple4. The flow contains high percent
water, F percent abrasive, and 1 percent air.
At the tubeEs top, the water is at the high speed calculated above. 'n fact, it is
highly supersonic with respect to the air. The air and abrasives are moving very
slowly in comparison. 2ithin the 6> ft.Csec. This acceleration is about 6@,>>>
times the acceleration of gravity, and it causes many abrasive grains to break. The
grains rub on and erode the mi4ing tubeEs sides. 7igure ).= shows the comple4,
sausage like wear pattern in a used mi4ing tube, indicating a very comple4 flow
pattern.
Fig 2.5: comple !lo" pa##e$%
+ikewise, the cutting process is comple4. The 3et e4it point lags the entrance
point by an amount that depends on the cutting speed. 't flops from side to side,
causing striations on the cut surface. 't produces a tapered kerf that ranges from
being widest at the top at high speed to widest at the bottom at low speed. &oreover,
the total kerf width depends on the cutting speed.
The H- and flow rate required to drive the 3et cutting process are determined
completely by the water no((le. o((le flow physics are well < known, and
quantities can be predicted accurately from scientific principles.
The flow in the mi4ing tube below the water no((le and in the material being
cut is comple4. *etermining it requires empirical study. 8esults of these empirical
studies often are proprietary, because machine manufacturers use this information to
compete on the ability to make good parts easily. However, this information is
embedded within the machinesE controllers and provides the user with the ability to
make e4cellent parts without detailed process knowledge.
1=
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).5 A8A0'$ -A8T'%+$0
).5.1%+A00'7'%AT': A* -8:-$8T'$0 :7 A8A0'$ &AT$8'A+0
A large number of different typos of abrasive materials are used in the
abrasive water< 3et technique. The evaluation of an abrasive material for abrasive
water.>>@# 1=)F.@)
0pessartine < 11.@15 ">.>>=# 1=@@.1=
-yrope < 11.6=D ">.>>=# 1=>5.BB
rossulare 5> 11.B@D ">.>>=# 1@D1.1B
Andradite B> < F> 1).>F1 ">.>>F# 1D@D.@1
0ince the abrasive particles erode the material and this is a mechanical
operation, which is a cross between the shearing and compressing the material by
the particle, it can be seen that the above characteri(ation of the particles is crucial.
The particles must be hard so that they are the erodes as opposed to being the
1@
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eroded. The shape is important. -articles with sharp edges can be envisioned to be
good cutters and upon impacting the material at one of their sharp edges can cause
high stress concentrations. 7ig. ).@ gives a few e4amples of shapes that would be
good for such purposes
7ig ).@? Typical shapes of garnet abrasive used for abrasive water
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turbulence of the 3et. Therefore much effort has gone into the Abrasive -article
*elivery 0ystem
Here are several other potential designs, two of which try to give theparticles speed either due to gravitational force or air pressure, and the other being a
design using a premi4 of the water and particles before 3et formation.
Fig 2./: 'a$#icle -a#e$ '$emi
Fig 2.0 Ab$a+i,e 'a$#icle $a,i# Fee3
1B
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Fig 2.14: Fo$ce3 Ai$ 'a$#icle Fee3
7or illustrative purposes 7ig. will be used since it is a basic model that
combines the 3et former, the mi4ing chamber and the collimator "which is also
known as the focus tube#. The top section is the e4iting straight portion of the 3et
former. Here the 3et e4its the no((le and enters into the mi4ing chamber. 7rom
ernoulli!s equation one can appro4imate the 3et speed into the chamber as?
2here - is the pressure developed in the straight portion of the 3et former
and r 2 is the density of the water. Here it is assumed that the pressure in the 3et
former is significantly greater than in the mi4ing chamber and the velocity of the
e4iting 3et into the mi4ing chamber is much greater than the fluid velocity in the 3et
former. 2ith these assumptions then the formula above is a good appro4imation to
the 3et speed as it enters the mi4ing chamber.
The abrasive particles are supplied from the right inlet tube and are pulled in
by a pressure differential created by the moving fluid past the inlet port "similar to
the lift developed on an aircraft wing as the air above the wing moves faster than the
air under the wing bottom thus creating an upward pressure potential or lift.# 7rom
1F
#@.)"...................
)> eqw
p
V th
=
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A simple conservation of momentum, the speed of the resulting abrasive
particle loaded water 3et can be estimated as
2here ma and mw are the mass flow rates of the abrasive particles and 3et water
respectively and Ais the speed of the abrasive water 3et as it enters the bottom
portion of the mi4ing chamber. 'n applying the conservation of momentum it has
been assumed that the impact of the 3et stream water and the abrasive particles is a
perfectly inelastic collision.
The purpose of the final reduced cross
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ABRASIVE WATER JETMACHINING VS OTHER METHODS
)1
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Chapter3A8A0'$ 2AT$8 $T &A%H'' 0 :TH$8&$TH:*0
7ig 5.1? Abrasive water 3et machining
Abrasive water 3et machining is a relatively new machining technique in thatit makes use of the impact of abrasive material to erode the work piece material. 't
relies on the water to accelerate the abrasive material and deliver the abrasive to the
work piece. 'n addition the water afterwards carries both the spent abrasive and the
eroded material away from the working area. %onventional machining practices
such as milling use a solid tool to cut the material usually by a shearing process.
%onventional machining may also use a liquid medium in con3unction with the
cutting tool but its purpose is not to deliver but to carry away the material. 'n
addition for both conventional and abrasive water 3et machining the liquid medium
will also act as a heat sink, taking heat away from the machining area.
5.1 %:&-A8' 2'TH +A0$80
Abrasive water 3ets can machine many materials that lasers cannot.
"8eflective materials in particular, such as Aluminum and %opper.
/niformity of material is not very important to an Abrasive 3et.
))
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Abrasive 3ets do not heat your part. Thus there is no thermal distortion or
hardening of the material.
-recision abrasive 3et machines can obtain about the same or higher
tolerances than lasers "especially as thickness increases#.
9our capital equipment costs for water 3et are generally much lower than that
for a laser. '.e. for the price of a laser, you can purchase several abrasive 3et1G ">.>)=mm# work,
but thatEs the e4ception, not the norm, and only on certain shapes and
materials.#
o heat affected Ione with Abrasive 3ets.
Abrasive 3ets require less setup.
&ake bigger parts.
&any $*& shops are also buying water 3ets. 2ater 3ets can be considered
to be like super
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same fi4turing on the $*& to do secondary operations and final cutting to
e4tra tolerance.
5.5 %:&-A8' 2'TH -+A0&A C 7'$ -+A0&A
Abrasive 3ets provide a nicer edge finish
Abrasive 3ets donEt heat the part
Abrasive 3ets can cut virtually any material
Abrasive 3ets are more precise
-lasma is typically faster
2ater 3ets would make a great compliment to a plasma shop where more
precision or higher quality is required or for parts where heating is not good,
or where there is a need to cut a wider range of materials.
Fig &.8: )o3e$% mac7i%e+ a$e $ela#i,el clea% a%3 9ie#.
5.6 %:&-A8' 2'TH 7+A&$ %/TT'
Abrasive 3ets provide a much nicer edge finish
Abrasive 3ets donEt heat the part
Abrasive 3ets can cut virtually any material
Abrasive 3ets are more precise
)@
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7lame cutting is typically faster
7lame cutting is typically cheaper, if you can use it.
2ater 3ets would make a great compliment to a flame cutting where more
precision or higher quality is required or for parts where heating is not good,
or where there is a need to cut a wider range of materials.
5.= %:&-A8' 2'TH &'++'
There is only one tool to qualify on an abrasive 3et
0etup and 7i4turing typically involves placing the material on the table with
an abrasive 3et
%leanup is much faster with an abrasive 3et
-rogramming is easier and faster
&achine virtually any material, including?
brittle materials
pre hardened materials
:therwise difficult materials such as Titanium, Hastalloy, 'nconel, 00 5>6,
hardened tool steel....
2ater 3ets are used a lot for complimenting or replacing milling operations.
They are used for roughing out parts prior to milling, for replacing milling
entirely, or for providing secondary machining on parts that 3ust came off the
mill. 7or this reason, many traditional machine shops are adding water 3et
capability to provide a competitive edge.
)D
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Fig &.: -7e% compa$i%g "i#7 milli%g
5.@ %:&-A8' 2'TH -/%H -8$00
+ower cost per piece for short runs
-lace holes closer to the materials edge
7ast turn
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Fig &.*: -7e% compa$e3 "i#7 p%c7 p$e++
Abrasive 3ets also play a big part as 3ust one part in a larger manufacturing process.
7or e4ample, abrasive 3ets are often used to machine features into an e4isting part, or
to do pre
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Chapter 4
A(RASIVE ET )AC;ININ
'n this process a focused stream of abrasive particles carried by high pressure
gas or air at a velocity of about )>> to 6>> mCsec is made to impinge on the work
surface through a o((le, and the work material is removed by erosion by the high
velocity of abrasive material removal rate which depends on flow rate and si(e of
abrasive particles. This process is best suited for machining super alloys and
refractory type of materials, and also machining thin sections of hard materials and
making intricate hard holes.
6.1 $lements of A..&.
The criteria used for evaluating the A..& process, vi(., material removal
rate, geometry of cut, are influenced by the following elements.
"i# o((le
"ii# Abrasives
"iii# elocity of fluid
5>
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"iv# 0tand off distance
"v# %arrier gas
6.1.1 o((le?
The abrasive particles are directed in to the work surface at high velocity
through no((le therefore, the material of the no((le is sub3ected to a great degree of
abrasion wear and hence these are made of hard materials.
Tungsten carbide no((les are used for circular cross section in the range of
>.1).B> mm diameter, and for rectangular section of si(e >.>B >.=> to >.1B
5.B mm
The rate of material removal and the si(e of the machined area are influenced
by the distance of the no((le from the work piece. The abrasive particles from the
no((le follow a parallel path only for a short distance and then the 3et floares
resulting in the aver si(ing of the hole. The material removal rate initially increases
with increase in the distance of the no((le from the work piece because of the
acceleration of particle after leaving the no((le. This increase is ma4imum up to a
distance of about Bmm and then it steadily drops off because of increase in
machining area of the some amount of abrasive and decrease in velocity of abrasive
particle stream due to drag.
7or precision machining, the no((les are provided with e4tended taper at the
tip in order to minimi(e secondary erosion by abrasive particles that rebound from
the work surface.
6.1.) 0tand off distance
0tand off distance plays a very important role in material removal rate in
A..&. as is evident from the e4perimental curve shown in fig.
51
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m.r.p
stand off distance
't is evident from fig. That the material removal rate increases with the
increase of tip distance up to a certain limit after which it remains unchanged for a
certain tip distance and then flows gradually. The stand off distance has also a
direct effect on the width of cut owing to the out ward flowing of the A. after a
short distance.
6.1.5 elocity of fluids
The velocity of the carrier gas converging the abrasive particles changes
considerably with the change of abrasive particle density as indicated in fig.
$4it velocity of gas
$4it velocity of gas %ritical velocity
Abrasive particle density
The e4it velocity of gas can be increased to critical velocity when the
internal gas pressure is nearly twice the pressure at the e4it of the no((le for an
abrasive particle density of (ero .'f the density of abrasive particles is gradually
increased, the e4it velocity will go on decreasing for the same pressure condition. 't
is due to fact that the kinetic energy of the fluid is utili(ed for transporting the
abrasive particles. However proper analysis is yet to be done in this regard.
5)
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7rom the above analysis, it is evident that the increased mass flow rate of
abrasive will result in a decreased velocity of fluid and will thereby cause a decrease
in the available energy for erosion and ultimately the material removal rate
.However, it is convenient to e4plain this fact with the help of a well defined term
known as mi4ing ratio.
&i4ing ratio =
6.1.6 %arrier gas
The carrier gas or propellant which is used in A..&. process is usually air,
carbon dio4ide "co2#, and nitrogen ")#, but never use o4ygen. %ommercial gas
cylinders can be employed satisfactorily.
The no((le pressure which generally affects the cutting process is generally
maintained between ) to B.= kgfCunit. Higher no((le pressure results in greater metal
removal rate, but it decreases the no((le life. The most suitable no((le pressure has
been found to be = kgfCunit.
6.) TH$ -H90'%0
1. 7ine particles ">.>)=mm# are accelerated in a gas stream "commonly air at a
few times atmospheric pressure#.
). The particles are directed towards the focus of machining "less than 1mm
from the tip#.
5. As the particles impact the surface, they fracture off other particles.
55
&ass flow rate of Abrasive
&ass flow rate of fluid or gas
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Fig 8.1: Ab$a+i,e 6e# mac7i%i%g
As the particle impacts the surface, it causes a small fracture, and the gas
stream carries both the abrasive particles and the fractured "wear# particles away.
rittle and fragile work pieces work better.
6.).1 The factors are in turn effected by
1. < The abrasive? composition; strength; si(e; mass flow rate
). < The gas composition, pressure and velocity
5. < The no((le? geometry; material; distance to work; inclination to work
6.).) The abrasive
1.
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1. < -ressure is typically >.) Cmm) to 1Cmm)
). < as composition effects pressure flow relationship
6.).6 o((le
1. < &ust be hard material to reduce wear by abrasives? 2% "lasts 1) to 5> hr#;
sapphire "lasts 5>> hr#
). < %ross sectional area of orifice is >.>=.) mm)
5. < :rifice can be round or rectangular
6. < Head can be straight, or at a right angle
Fig 8.2: Tpe+ o! %o
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6.5 TH$ 8$+AT':0H'- $T2$$ H$A*, A* :II+$ T'-
*'0TA%$.
Fig 8.&: $ela#io%+7ip be#"ee% 7ea3= a%3 %o
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6.= 0/&&A89 :7 A& %HA8A%T$8'0T'%0
1. &echanics of material removal < brittle fracture by impinging abrasive grains
at high speed
). &edia < Air, %:)
5. Abrasives? Al):5, 0ic, >.>)=mm diameter, )gCmin, non> mCsec
=. -ressure L ) to 1> atm.
@. o((le < 2%, sapphire, orifice area >.>=.) mm), life 1)> hr., no((le tip
distance >.)=. +imitations < low metal removal rate "6> mgCmin, 1= mm5Cmin#, embedding
of abrasive in work piece, tapering of drilled holes, possibility of stray
abrasive action.
6.@ -8:%$00 %HA8A%T$8'0T'%0
6.@.1 &$TA+ 8$&:A+ 8AT$
A typical material removal rate for abrasive 3et machining is 1@ mm5Cmin in
cutting glass. A minimum practical width of cut of about >.1 mm cab be obtained by
using a rectangular no((le with an orifice of >.>D=>.= mm placed at a distance of
>.>B mm.
Abrasive 3et machining is a finishing process that removes material from work
pieces by focusing a high speed stream of abrasive particles carried in an air 3et.
/ses a high velocity stream of abrasive particles carried in an air or gas 3et
's used for machining delicate or very hard materials
5D
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o((les are usually made of tungsten or sapphire to resist abrasion
-roduces a taper in deep cuts
*istance of no((le from work piece affects the si(e of the machined area.
Fig 8.: Ac#io% o! ab$a+i,e pa$#icle+ o% "o$> piece
Fig 8.*: +7o"+ #7e "o$> piece mac7i%e3 b A)
6.@.) Accuracy and surface finish
2ith close control of the various parameters a tolerance in the region of
>.>= mm can be obtained. :n normal production work an accuracy of >.1 mm is
5B
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easily held. &asking to define the machining area is sometimes used go prevent
stray cutting. %opper, glass and rubber are used as masking materials. 8ubber has a
good life but has gives poor definition. The corner radius obtained can be limited to
>.1 mm. taper is around >.>= mm per 1>mm penetration.
The surface finish ranges from >.6mm# thick part may take hours.
A 1C1@G "1.=mm# part will cut in seconds
6.D $T 2H$ 'T $K'T0 TH$ :II+$
+ike a fire hose. The 3et starts out coherent, then fans out. 2hen cutting
thick metal, the 3et will be held coherent by the metal you are cutting.
5F
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Fig 8./: e# "7e% i# ei#+ #7e %o
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eneral purpose machine shops? Here is where ' see the biggest growth in abrasive
3et use. This is because abrasive 3ets are such good all
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&odel shops C rapid prototyping? 7ast turn around of single piece production
in nearly any material makes water 3ets great for these kinds of applications.
2ealthy hobbyists? ' have seen a few people buy them for their homes. '
want one in my garage too.
0chools? &any of the larger si(e universities that offer engineering classes
also have water 3ets. They are great tools for the classroom environment
because they are easy to learn, program, and operate, and because they can
make one
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FABRICATION OF MODEL FORABRASIVE JET MACHINING
65
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Chapter 57A8'%AT': :7 &:*$+ 7:8 A8A0'$ $T
&A%H''
The e4perimental set up of abrasive 3et cutting machine is consists of air
compressor of ma4 pressure allowed is D kgCcm). The abrasive powder silicon
carbide is supplied from a hopper. The hopper is made of galvani(ed iron sheet. The
outlet of hopper is connected to a >.=.=
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5
= 6 ) 1
@
6=
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1. %ompressor
). all valve
5. Hopper
6. 'nclined T 3oint
=. -ipe line
@. o((le
6@
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PROCESS VARIABLES INABRASIVE JET MACHINING
6D
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Chapter 6-8:%$00 A8'A+$0 ' A8A0'$ $T &A%H''
@.1 -$87:8&A%$ :7 A8A0'$ $T &A%H''
The performance of A..&. is 3udged by the following
&etal removal rate
7inish of the work piece
8ate of wear of the no((le
@.1.1 &etal removal rate in A..&
Taking into consideration the fact that metal removal is due to the chipping
of the work surface brought about by the impacting abrasive particles. &athematical
model for the computation of the metal removal rate in A&. They have shown that
the rate of metal removal J in A& can be obtained by $q.
#1.@".........1)
6C5
)C55
6 eqavNdKQ
y
=
7rom eq it can be seen that
#).@"....)C5 eqNvQAs a first degree appro4imation, i can be assumed that
#5.@"......eqpN
#6.@".......)C1 eqpv
Therefore#=.@".........1>D= eqpQ
@.1.1.1 TH$ 7A%T:80 A77$%T' &$TA+ 8$&:A+ 8AT$
The variables that influence the rate of metal removal and accuracy of
machining in this process ate?
"i# %arrier gas.
6B
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should be so designed that the pressure loss due to bends, friction, etc. is as little as
possible.
CONCLUSION
=1
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The abrasives used for cutting are aluminum o4ide and silicon carbide where
as sodium bi
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